Network planning under uncertainty with an application to hydropower generation

Summary We present a general modeling framework for therobust optimization of linear network problems with uncertainty in the values of the right-hand side. In contrast to traditional approaches in mathematical programming, we use scenarios to characterize the uncertainty. Solutions are obtained for each scenario and these individual scenarios are aggregated to yield a nonanticipative or implementable policy that minimizes the regret of wrong decisions. A given solution is termed robust if it minimizes the sum over the scenarios of the weighted upper difference between the objective function value for the solution and the objective function value for the optimal solution for each scenario, while satisfying certain nonanticipativity constraints. This approach results in a huge model with a network submodel per scenario plus coupling constraints. Several decomposition approaches are considered, namely Dantzig-Wolfe decomposition, various types of Benders decomposition and different quadratic network approaches for approximating Augmented Lagrangian decomposition. We present computational results for these methods, including two implementation versions of the Lagrangian based method: a sequential implementation and a parallel implementation on a network of three workstations.     

On modelling the maximum workload allocation for parallel unrelated machines with setups

Consider a manufacturing process in which a group of machines (or people) perform a single operation on a number of different parts. The processing time depends on both the part and the machine. In addition, each machine requires significant setup time between processing different part types. The problem consists of obtaining a feasible allocation of parts to machines such that the makespan (i.e. greatest machine workload) is minimized. We present two equivalent 0–1 models. The first model arises by considering the assignment of individual parts to machines. It is amenable to Lagrangian decomposition techniques. The second model is more hierarchical in nature; it considers the two options of assigning an entire part type to a single machine, or of splitting the type across machines. The second model is more amenable than the first to branch-and-bound techniques. We report about our computational experience for finding lower bounds of the optimal solution by appending violated cuts and, ultimately, obtaining the optimal solution of real-life problems.     

Designing SISO observers with unknown input

In this paper we investigate the observer design for Single-InputSingle-Output (SISO) systems with unknown input. We find thatthe design conditions proposed by several authors in the pastlead to unity relative degree of the plant and zeros of theplant in the open left half of the complex plane, for SISO systems.In other words an observer for a SISO plant with unknown inputcan be designed if and only if the plant is of unity relativedegree and the numerator of the transfer function is Hurwitz.These conditions have an interesting consequence in the contextof model reference adaptive control (MRAC) for the case of relativedegree one, in the sense that strictly real positive (SPR) conditionfor the model reference is not needed.     

Kinetics and mechanisms of the permanganate oxidation of L-valine in neutral aqueous solutions

The permanganate oxidation of L-valine has been studied by visible spectrophotometry in neutral aqueous solutions. Under these conditions, both the zwitterionic and anionic forms of the amino acid are oxidized, the reaction being autocatalyzed by soluble colloidal manganese dioxide. Kinetic data for both the uncatalyzed and autocatalytic reaction pathways have been obtained, and reaction sequences consistent with the experimental findings are proposed.     

SXRP: an X-ray polarimeter for the SPECTRUM-X-Gamma Mission

Summary TheStellar X-ray Polarimeter (SXRP) is a focal plane instrument which will be flown on the SPECTRUM-X-Gamma mission in 1993. The polarimeter is composed of two separate instruments: the first exploits the dependence on the polarization of the Bragg reflection from a graphite crystal, and of the Thomson scattering from a metallic lithium target. The second instrument makes use of the recently discovered polarization dependence of X-ray photoemission from CsI. The SXRP will permit sensitive measurements of several hundreds of known X-ray sources. X-ray polarization measurements will allow us to constrain the physical mechanisms and the geometries of several classes of galactic X-ray sources, such as X-ray pulsars, black-hole candidates and supernova remnants. Moreover, and for the first time, SXRP will be able to perform highly sensitive measurements of the brightest extragalactic sources. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Preconcentration and determination of mercury(II) at a chemically modified electrode containing 3-(2-thioimidazolyl)propyl silica gel.

A mercury-sensitive chemically modified graphite paste electrode was constructed by incorporating modified silica gel into a conventional graphite paste electrode. The functional group attached to the (3-chloropropyl) silica gel surface was 2-mercaptoimidazole, giving a new product denoted by 3-(2-thioimidazolyl)propyl silica gel, which is able to complex mercury ions. Mercury was chemically adsorbed on the modified graphite paste electrode containing 3-(2-thioimidazolyl)propyl silica (TIPSG GPE) by immersion in a Hg(II) solution, and the resultant surface was characterized by cyclic and differential pulse anodic stripping voltammetry. One cathodic peak at 0.1 V and other anodic peak at 0.34 V were observed on scanning the potential from -0.1 to 0.8 V (0.01 M KNO3; v = 2.0 mV s(-1) vs. Ag/AgCl). The anodic peak at 0.34 V show an excellent sensitivity for Hg(II) ions in the presence of several foreign ions. A calibration graph covering the concentration range from 0.02 to 2 mg L(-1) was obtained. The detection limit was estimated to be 5 microg L(-1). The precision for six determinations of 0.05 and 0.26 mg L(-1) Hg(II) was 3.0 and 2.5% (relative standard deviation), respectively. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

EPR of Er3+, Nd3+, and Ce3+ ions in YAlO3 single crystals

EPR spectra of the Er³⁺, Nd³⁺, and Ce³⁺ ions substituting for the Y³⁺ ion in the YAlO₃ yttrium orthoaluminate lattice are studied. The EPR spectra of these rare-earth ions are described by a spin Hamiltonian of rhombic symmetry with an effective spin S=1/2. The principal values of the g tensors were determined from an analysis of the angular dependences of the EPR spectra. The orientation of the local magnetic axes of paramagnetic centers relative to the YAlO₃ crystallographic directions are shown to depend on the actual rare-earth species. The EPR spectra exhibit a hyperfine structure due to the ¹⁶⁷Er, ¹⁴³Nd, and ¹⁴⁵Nd odd isotopes, which permitted unambiguous identification of these spectra. The hyperfine coupling constants for the odd erbium and neodymium isotopes are determined.     

Jahn-Teller calculations for CuO4 and FeO4 clusters in the Nd1.85Ce0.15Cu0.99Fe0.01O4−δ

The Jahn-Teller distortion mechanism in the Nd_2?x Ce _x CuO₄ is analyzed. This analysis is based on a quasi-molecular model for the CuO₄ cluster havingD _4h symmetry. In order to compare with experimental Mössbauer measurements in the doped Nd_1.85Ce_0.15Cu_0.99Fe_0.01O_4?δ superconductor, the FeO₄ cluster is also analyzed for the case of Fe²⁺ in the high spin state. The results show not evidence of a Jahn-Teller effect in these superconductors.     

Spectrophotometric determination of total vicinal diketones with isoniazide and a zirconium salt

Summary A method has been worked out for the spectrophotometric determination of total vicinal diketones.It is based on the distillation of diacetyl and/or 2,3-pentanedione, the subsequent condensation with isoniazide (yielding the corresponding hydrazones), the complexation with zirconium(IV) and the photometric measurement of the resulting yellow complexes at 410 nm. The two reactions were studied separately. Variables such as pH, heating time, and excess reactives are discussed. The method may be used for the determination of these compounds in foods.     

Regional Variations in Energy Consumption of Appliances: Conditional Demand Analysis Applied to Brazilian Households

Estimating the true consumption of appliances in use is important both for modeling and short term forecasting of electricity demand, as well as for planning and assessing Demand Side Management (DSM). This paper applies the new technique known as Conditional Demand Analysis (CDA) to estimate consumption of these appliances. This was made possible due to a major survey carried out for the Brazilian National Electricity Conservation Program by the Brazilian electric utility companies while they were still state owned. Results were checked against traditional appliance energy consumption figures, and investigations carried out to ascertain if differences were due to regional variations in consumption patterns from northern to southern Brazil.